A rapid-actuation braking device, also referred to as a reduced dead travel braking device, is known from the prior art and comprises a master cylinder actuated by a control rod actuated by a driver, the action of the driver being amplified by a pneumatic booster by means of which it is possible to reduce the pedal travel necessary to obtain a braking action.
The booster of known type, described for example in document FR 2 696 143, comprises a casing in which a skirt dividing the inner space of the casing into a low-pressure chamber and a variable-pressure chamber is slideably mounted in a sealed manner.
The skirt comprises a central passage in which is mounted a pneumatic piston provided with a three-way valve arrangement controlled by the control rod, placing the low-pressure chamber and the working chamber at rest in communication, and isolating the low-pressure chamber from the working chamber and placing the working chamber in communication with a high-pressure fluid source.
The skirt is mounted so that it can move axially with respect to the pneumatic piston over a defined travel at the start of braking. Consequently, when the driver presses on the brake pedal, the working chamber is isolated from the low-pressure chamber and fills with high-pressure pneumatic fluid. Owing to the pressure differential between the low-pressure chamber and the working chamber, the skirt moves into the low-pressure chamber without taking along the pneumatic piston over the defined travel. Consequently, the driver does not have to depress the pedal further to keep the working chamber supplied with high-pressure pneumatic fluid. The movement of the skirt is transmitted to a primary piston of a master cylinder, causing the valves of the master cylinder to close and the pressure at the brakes to rise.
Beyond the defined travel, the skirt bears on a radially external part of the pneumatic piston, their movements then being connected. From this moment, the driver must depress the control rod further to obtain an increase in the braking intensity. Following the selection of the dead travel, the driver will not be able to tell from the brake pedal the travel required to close the valves of the master cylinder, this travel, also referred to as dead travel, not producing any rise in pressure in the brakes, or the driver will directly feel a strong deceleration, giving the sensation of applied braking.
This device, referred to as a concealed dead travel device since it conceals the dead travels from the driver, is entirely satisfactory but continues to form the subject of research to simplify it in order to reduce its complexity, make it easier to assemble and also reduce its cost price. The device is thus structurally extremely complex since it requires contorting the pneumatic piston and a multi-pass stamping operation has to be carried out.